High-velocity gun propellants containing solid nitrogen hydrides or boron compounds



United States Patent 3,444,013 HIGH-VELOCITY GUN PROPELLANTS CONTAIN-ING SOLID NITROGEN HYDRIDES R BORON COMPOUNDS Joseph Green, Dover, andPaul F. Schaetrer, Denville, NaL, assignors to Thiokol ChemicalCorporation, Trenton, N .J a corporation of Delaware No Drawing. FiledDec. 3, 1964, Ser. No. 416,683 Int. Cl. C0611 /00 U.S. Cl. 149-22 5Claims The present .invention relates to novel compositions adapted foruse as ballistic propellants and especially advantageous for use ashypervelocity gun propellants. This invention also relates to cartridgescomprising such propellants.

The term hypervelocity is used in relation to the terms low-velocityguns and high-velocity guns into which artillery has been roughlydivided. Low-velocity guns are those from which projectiles are fired atnot much higher than 2000 feet per second; high-velocity guns are thosefrom which projectiles are fired at up to about 3000 feet per second.The term hypervelocity is used to refer to muzzle velocities of 3500feet per second or higher.

. Ballistic projectiles having hypervelocity have long been considereddesirable for both military and domestic uses. Discharging a projectilesuch as a bullet, shell, etc., from a weapon at high velocity has anumber of advantages. For example, higher projectile speed can result inlonger range and improved penetration of armored objects. Furthermore,improved accuracy may be obtained when using hypervelocity projectiles.This improved accuracy is due to such factors as (l) the allowance of aflatter ballistic trajectory and (2) the reduction of time betweenfiring and target impact. This reduction in time is important, not onlybecause the target will have less time to change position, but alsobecause the time in which outside forces such as wind, etc., may act onthe projectile is reduced.

There are a number of practical problems which hindered the wide scaleuse of hypervelocity weapon systems. Erosion of the gun itself ispromoted by the high temperatures and pressures ordinarily required forobtaining hypervelocity projectiles with conventional gun propellants.In moderate size weapons, only a few rounds may be fired before theenlargement of the bore becomes a problem and interferes with theaccurate aiming of subsequent rounds. In a 12-inch gun about a pound ofmaterial is often removed on firing a single round at a muzzle velocityof 2600 feet per second. This erosion would be several times greaterwere the velocity increased a 50 percent, i.e., to 3900 feet per second.

Furthermore, high temperatures required for hypervelocity projectilesenergized with conventional gun propellants also contribute to theerosion problem. This is especially true when the rate of fire is high.Moreover, the high temperatures per se are undesirable. In machine gunsfor example, barrels often heat to 750 C. and more, swell, bend, andoften blow up.

Therefore, it is readily seen that projectiles may not be firedrepeatedly at hypervelocities with any degree of accuracy from gunbarrels which are subjected to the aforementioned severe stresses.Projectiles are normally afforded stability in flight by a spinningmotion imparted by the rifiing in the bore of the gun to the projectileby means of a rotating band on the projectile. An additional problemwhich is encountered when sufiicient conventional propellant is fired toprovide hypervelocity to a projectile is the frequent exceeding of thestrength limit of this rotating band by the high pressure andtemperature "ice conditions; thus, band failure may limit the muzzlevelocities attainable with conventional propellants.

All of these problems arise not from the velocity of the projectileitself, but only from the extreme conditions existing in the bore of agun when sufiicient conventional propellant is burned to imparthypervelocity to a projectile.

It is apparent that a propellant which could be utilized to imparthigher velocity projectiles with lower temperatures and pressures in thegun barrel would not only be useful in improved marksmanship but alsowould allow a significant decrease in gun erosion.

It is known that the maximum muzzle velocity obtainable with a givencharge of propellant will be determined by the distribution of kineticenergy released by the decomposition of the propellant between theprojectile and the propellant gas. That part of the kinetic energyimparted to the gas will be determined in large part by its molecularweight. Assuming the projectile mass has been reduced to the minimummass adequate for a particular use, it is seen that the muzzle velocityobtainable is determined in large part by the molecular weight of thegas. The lighter the gas, the greater the muzzle velocity will be. Theweight of the combustion products of the nitro cellulose powder, atypical conventional propellant, is about 28. In general, conventionalpropellants decompose to gases having molecular weights from about 25 to28.

It is an object of this invention to provide propellant compositionsadapted for obtaining hypervelocity projectiles. It is another object ofthis invention to provide dependable propellant compositions ofrelatively low molecular weight. It is still another object of thisinvention to provide gun propellants adapted for low temperature and lowpressure operation. It is still a further object of this invention toprovide cartridges comprising the aforementioned gun propellants. It isa still further object of the invention to provide .a propellant whichcontains a higher energy content per unit mass than conventionalpropellants.

Applicants have met these objects by providing low molecular weightpropellant compositions having favorable thermodynamic characteristicsand favorable chemical characteristics so as to avoid undue erosion ofgun barrels. The propellant comprises boron-containing nitrogencompounds which yield BN+hydrogen gas on decomposition and nitrogenhydrides yielding N and H on dc.- composition.

The primary ingredients in applicants propellant composition arehydrogen-nitrogen-boron compounds and/or solid nitrogen hydridecompounds such as hydrazine bisborane, diammonodecaborane (B N Hdiammonodecaborane hydrazinate (B N H and dihydraziniumperhydrodecaborane. Other propellants that c an be utilized in formingthe propellant compositions include nitrogen hydrides which yield N andH gases upon combustion such as hydrazinium azide andtriaminoguanidinium azide can also be used.

Minor portions of other atoms may be found in such compounds, but thequantity is too small to affect the favorable properties of thepropellant.

These propellant-forming compounds are characterized by their lowisochoric flame temperature, advantageously less than 2300 K. and thelow molecular weight of the gases formed 'by their decomposition,preferably a mole formed for each 16 grams or less of thepropellant-forming compound.

In general, these compounds may be broken down into two types, thosedecomposing into BN and hydrogen and those decomposing into hydrogen andnitrogen.

Of course, to be useful as propellants it is also nec essary that thecompounds formed in the gun breech and barrel are not excessivelycorrosive and are sufficiently dense so that a sufficient quantity ofpropellant may be inse'rted into the gun for effective firing. Theabove-identified compounds meet these qualifications and are therebyuniquely advantageous for use as propellants in hypervelocity ballisticapplications.

To demonstrate the improved ballistic properties of these newpropellants, the following data, obtained in a test firing is presented.Propellant A is formulated of 80 parts hydrazine bisborane, 20 partsnitrocellulose and one part graphite. The pellets had a 0.25 inchdiameter, a 0.063 inch diameter core therein, and a density of 0.82 gramper cc. Propellant B is a commercial single-base standard sold'underthe'trade name'IMR 4227. The'difierence in propellant weight used ineach test is due to the different densities of the propellants. Eachsetof data 'represents the average of three firings. Cartridges withpropellant A were primed with magnum primer of the trade name CCI 250obtainable from Cascade Cartridge Inc.

Thus it is seen that applicants novel propellant with only one-half themass charge of the standard propellant causes the projectile to leavethe muzzle at a speed nearly 38% faster than the speed imparted by thestandard propellant. Moreover, the pressure reached in the gun on firingof the standard propellant is about 11% higher than that caused byapplicants propellant. Moreover, the total amount of kinetic energyimparted to the projectile is 90% greater when 83.8 grains of applicantspropellant is used than when 160 grains of the standard is utilized.

This improvement in performance has been found to be due in part to thelow molecular weight of the novel propellants which contributes to theirfavorable low heatgenerating properties.

When applicants compounds are compared with standards such as thecommercially available Hercules Bullseye propellant (a commercialdouble-base propellant containing 40% nitroglycerin) and thecommercially available M-lO propellant (a single base propellantcontaining 98% of nitrocellulose), the importance of the low molecularweight decomposition products is made more evident.

T K. is the isochoric flame temperature. M is the average molecularweight of the products produced by decomposition of the propellant.

It is clear that applicants propellants provide larger quantities of gasand provide for greater impetus at far lower flame temperatures than thestandard propellants.

Compositions comprising these unique and energetic gun propellantsshould also preferably include minor amounts of compounding additives.For example lubricants like stearic acid, metal stearates, magnesiumsilicate and metal carbonates aid in contributing compacting andfree-flowing properties to the compositions so that they may be moreeasily manufactured into grains having optimum configuration. Amongother additives are silica powders like that known to the art by thetrade name Cab-O-Sil, complexes of silica and aluminum oxide,diatomaceous earth and other such antiblock additives known to the art.

Initiators usefully incorporated into these compositions includenitrocellulose-based blank-fire powder, polyethylene hydrazine nitrate,and ethylenedi(aminoguanidinium)- azide/ formaldehyde copolymer.Initiators are usually necessary for the hydrazine-bisborane basedpropellants and should be incorporated in levels of up to 10 to 30% ormore based on the total Weight of initiator and hydrazinebisborane.Nitrocellulose is a particularly useful material.

When it is desirable to lower the burning rate of the propellant, smallquantities of burning rate modifiers known to the art may beincorporated. For example, graphite is often conveniently used in suchformulations.

A number of processing problems must be overcome in order to producepropellants containing reactive boroncontaining compounds such ashydrazine bisborane or reactive compound like hydrazinium azide.

Nitrocellulose, when used in the compositions, must be incorporated intothe process in a nonaqueous medium because both hydrazinium azide andhydrazine bisborane Will bedegraded by water. A hydrocarbon such ashexane V An ester such as propyl acetate and/ or ethyl acetate,preferably diluted by a hydrocarbon, is used as a solvent medium formixing about a 10% lacquer of nitrocellulose *with reactiveboron-containing compounds. Conventional ether/ alcohol mixtures are notacceptable because of their reactivity.

The mixing operation is carried out in a mixer of the type known to theart, for example a Baker-Perkins planetary vertical mixer. It isnecessary, of course, to provide an explosion barrier between themixture and any attendant personnel. The mixer is fitted with vacuumfittings and excess ester solvent and hydrocarbon are evaporated undervacuum before the mixture is extruded into propellant grains.

Additives such as graphite and burning rate modifiers are convenientlyadded to the mix after up to three hours of processing, i.e., just priorto extrusion.

Extrusion of the propellant grains can be carried out by a Loomisextrusion press of a 7-ton capacity in a manner known to the art.Another method of fabricating grains is to press pellets of the requiredsize with or without perforations using a pellet press such as a Stokespellet press.

We claim:

1. A gun propellant comprising granules of a mixture of a gas-formingconstituent consisting of at least one member selected from the groupconsisting of hydrogennitrogen-boron compounds and normally solidnitrogen hydrides and a minor amount of a molding lubricant.

2. A gun propellant comprising as its essential gasforming compounds amajor portion of hydrazine bisborane and a minor portion ofnitrocellulose.

3. The process of forming gun propellants having hydrogen-nitrogen-boroncompounds and nitrocellulose as their essential gas-forming constituentscomprising wetting nitrocellulose in a nonpolar solvent With saidsolvent, mixing said nitrocellulose into an ester-based lacquer,admixing said lacquer with said boron-containing compound to form amixture in which the solids comprise a major proportion of theboron-containing compounds and a minor proportion of nitrocellulose, anddrying excess solent from the mixture.

4. A gun propellant comprising granules of a mixture of a gas-formingconstituent consisting of at least one member selected from the groupconsisting of hydrazine bisborane, hydrazinium azide,diammonodecaborane, diammonodecaborane hydrazinate, dihydraziniumperhydrodecaborane, and triaminoguanidinium azide, and a minor amount ofa molding lubricant.

5. A gun propellant comprising as its essential gasforrning compounds amajor proportion of hydrazinium azide and a minor proportion ofnitrocellulose.

References Cited UNITED STATES PATENTS 3,148,938 9/1964 Knoth 149-22X3,153,567 10/1964 Fetter.

6 3,170,283 2/1965 Sayles 149-36 X 3,250,651 5/1966 Bell et a1 149-22 X3,268,376 8/1966 Haldeman et al 149-22 X 5 BENJAMIN R. PADGE'IT, PrimaryExaminer.

US. Cl. X.R. 149-18, 36, 94

1. A GUN PROPELLANT COMPRISING GRANULESS OF A MIXTURE OF A GAS-FORMINGCONSTITUENT CONSISTING OF HYDROGENNITROGEN-BORON COMPOUNDS AND NORMALLYSOLID NITROGEN HYDRIDES AND A MINOR AMOUNT OF A MOLDING LUUBRICANT.